Causal Diagrams: Pitfalls and Tips

Graphical models are useful tools in causal inference, and causal directed acyclic graphs (DAGs) are used extensively to determine the variables for which it is sufficient to control for confounding to estimate causal effects. We discuss the following ten pitfalls and tips that are easily overlooked when using DAGs: 1) Each node on DAGs corresponds to a random variable and not its realized values; 2) The presence or absence of arrows in DAGs corresponds to the presence or absence of individual causal effect in the population; 3) "Non-manipulable" variables and their arrows should be drawn with care; 4) It is preferable to draw DAGs for the total population, rather than for the exposed or unexposed groups; 5) DAGs are primarily useful to examine the presence of confounding in distribution in the notion of confounding in expectation; 6) Although DAGs provide qualitative differences of causal structures, they cannot describe details of how to adjust for confounding; 7) DAGs can be used to illustrate the consequences of matching and the appropriate handling of matched variables in cohort and case-control studies; 8) When explicitly accounting for temporal order in DAGs, it is necessary to use separate nodes for each timing; 9) In certain cases, DAGs with signed edges can be used in drawing conclusions about the direction of bias; and 10) DAGs can be (and should be) used to describe not only confounding bias but also other forms of bias. We also discuss recent developments of graphical models and their future directions

Trends in Geographic Distribution of Nursing Staff in Japan from 2000 to 2010:A Multilevel Analysis

The aim of this study was to examine trends in the geographic distribution of nursing staff in Japan from 2000 to 2010. We examined time trends in the rates of nursing staff per 100,000 population across 349 secondary health service areas. Using the Gini coefficient as a measure of inequality, we separately analyzed the data of 4 nursing staff types:public health nurses (PHN), midwives (MW), nurses (NS), and associate nurses (AN). Then, using multilevel Poisson regression models, we calculated the rate ratios (RRs) and their 95% confidence intervals (CIs) for each type of nursing staff per 1-year change. Overall, the distribution of PHN, MW, and NS improved slightly in terms of the Gini coefficient. After adjusting for prefectural capital and population density, PHN, MW, and NS significantly increased;the RRs per 1-year increment were 1.022 (95% CI:1.020-1.023), 1.021 (95% CI:1.019-1.022), and 1.037 (95% CI:1.037-1.038), respectively. In contrast, AN significantly decreased;the RR per 1-year increment was 0.993 (95% CI:0.993-0.994). Despite the considerable increase in the absolute number of nursing staff in Japan (excluding AN), this increase did not lead to a sufficient improvement in distribution over the last decade

Thyroid Cancer Detection by Ultrasound Among Residents Ages 18 Years and Younger in Fukushima

Background: After the Great East Japan Earthquake and Tsunami in March 2011, radioactive elements were released from the Fukushima Daiichi Nuclear Power Plant. Based on prior knowledge, concern emerged about whether an increased incidence of thyroid cancer among exposed residents would occur as a result. Methods: After the release, Fukushima Prefecture performed ultrasound thyroid screening on all residents ages <=18 years. The first round of screening included 298,577 examinees, and a second round began in April 2014. We analyzed the prefecture results from the first and second round up to December 31, 2014, in comparison with the Japanese annual incidence and the incidence within a reference area in Fukushima Prefecture. Results: The highest incidence rate ratio, using a latency period of 4 years, was observed in the central middle district of the prefecture compared with the Japanese annual incidence (incidence rate ratio = 50; 95% confidence interval [CI] = 25, 90). The prevalence of thyroid cancer was 605 per million examinees (95% CI = 302, 1,082) and the prevalence odds ratio compared with the reference district in Fukushima Prefecture was 2.6 (95% CI = 0.99, 7.0). In the second screening round, even under the assumption that the rest of examinees were disease free, an incidence rate ratio of 12 has already been observed (95% CI = 5.1, 23). Conclusions: An excess of thyroid cancer has been detected by ultrasound among children and adolescents in Fukushima Prefecture within 4 years of the release, and is unlikely to be explained by a screening surge

Shift Work and Diabetes Mellitus among Male Workers in Japan:Does the Intensity of Shift Work Matter?

The purpose of this study was to examine the association between shift work and diabetes mellitus by separating shift workers according to the intensity of their shift work (seasonal shift work and continuous shift work). Between May and October 2009, we collected data from annual health checkups and questionnaires at a manufacturing company in Shizuoka, Japan. Questionnaires were returned by 1,601 workers (response rate:96.2%, men/women＝1,314/287). Diabetes mellitus was defined as hemoglobin A1c≥6.5% and fasting blood sugar≥126mg/dl. After exclusions, which included all the women and clerical workers because they did not work in shifts, we analyzed 475 skilled male workers. After adjusting for age, smoking status, frequency of alcohol consumption, and cohabitation status, odds ratios for diabetes mellitus were 0.98 (95% confidence interval [CI]:0.28-4.81) and 2.10 (95% CI:0.77-5.71) among seasonal shift workers and continuous shift workers, respectively, compared with non-shift workers. In an age-stratified analysis (＜45 years vs.≥45 years), the association between continuous shift work and diabetes mellitus was more pronounced among older participants. Compared with non-shift workers, the risk of diabetes mellitus was increased among continuous shift workers, whereas its effect is limited among seasonal shift workers

Social and Geographical Inequalities in Suicide in Japan from 1975 through 2005: A Census-Based Longitudinal Analysis

Background: Despite advances in our understanding of the countercyclical association between economic contraction and suicide, less is known about the levels of and changes in inequalities in suicide. The authors examined social and geographical inequalities in suicide in Japan from 1975 through 2005. Methods: Based on quinquennial vital statistics and census data, the authors analyzed the entire population aged 25–64 years. The total number of suicides was 75,840 men and 30,487 women. For each sex, the authors estimated odds ratios (ORs) and 95% credible intervals (CIs) for suicide using multilevel logistic regression models with “cells” (cross-tabulated by age and occupation) at level 1, seven different years at level 2, and 47 prefectures at level 3. Prefecture-level variance was used as an estimate of geographical inequalities in suicide. Results: Adjusting for age and time-trends, the lowest odds for suicide was observed among production process and related workers (the reference group) in both sexes. The highest OR for men was 2.52 (95% CI: 2.43, 2.61) among service workers, whereas the highest OR for women was 9.24 (95% CI: 7.03, 12.13) among security workers. The degree of occupational inequalities increased among men with a striking change in the pattern. Among women, we observed a steady decline in suicide risk across all occupations, except for administrative and managerial workers and transport and communication workers. After adjusting for individual age, occupation, and time-trends, prefecture-specific ORs ranged from 0.76 (Nara Prefecture) to 1.36 (Akita Prefecture) for men and from 0.79 (Kanagawa Prefecture) to 1.22 (Akita Prefecture) for women. Geographical inequalities have increased primarily among men since 1995. Conclusions: The present findings demonstrate a striking temporal change in the pattern of social inequalities in suicide among men. Further, geographical inequalities in suicide have considerably increased across 47 prefectures, primarily among men, since 1995

Social and Geographic Inequalities in Premature Adult Mortality in Japan: A Multilevel Observational Study from 1970 to 2005

Objectives: To examine trends in social and geographic inequalities in all-cause premature adult mortality in Japan. Design: Observational study of the vital statistics and the census data. Setting: Japan. Participants: Entire population aged 25 years or older and less than 65 years in 1970, 1975, 1980, 1985, 1990, 1995, 2000 and 2005. The total number of decedents was 984 022 and 532 223 in men and women, respectively. Main outcome measures: For each sex, ORs and 95% CIs for mortality were estimated by using multilevel logistic regression models with ‘cells’ (cross-tabulated by age and occupation) at level 1, 8 years at level 2 and 47 prefectures at level 3. The prefecture-level variance was used as an estimate of geographic inequalities of mortality. Results: Adjusting for age and time-trends, compared with production process and related workers, ORs ranged from 0.97 (95% CI 0.96 to 0.98) among administrative and managerial workers to 2.22 (95% CI 2.19 to 2.24) among service workers in men. By contrast, in women, the lowest odds for mortality was observed among production process and related workers (reference), while the highest OR was 12.22 (95% CI 11.40 to 13.10) among security workers. The degree of occupational inequality increased in both sexes. Higher occupational groups did not experience reductions in mortality throughout the period and was overtaken by lower occupational groups in the early 1990s, among men. Conditional on individual age and occupation, overall geographic inequalities of mortality were relatively small in both sexes; the ORs ranged from 0.87 (Okinawa) to 1.13 (Aomori) for men and from 0.84 (Kanagawa) to 1.11 (Kagoshima) for women, even though there is a suggestion of increasing inequalities across prefectures since 1995 in both sexes. Conclusions: The present findings suggest that both social and geographic inequalities in all-cause mortality have increased in Japan during the last 3 decades

Diarrhea and related personal characteristics among Japanese university students studying abroad in intermediate- and low-risk countries

Despite an increasing number of students studying abroad worldwide, evidence about health risks while they are abroad is limited. Diarrhea is considered the most common travelers' illness, which would also apply to students studying abroad. We examined diarrhea and related personal characteristics among Japanese students studying abroad. Japanese university students who participated in short-term study abroad programs between summer 2016 and spring 2018 were targeted (n = 825, 6-38 travel days). Based on a 2-week-risk of diarrhea (passing three or more loose or liquid stools per day) among travelers by country, the destination was separated into intermediate- and low-risk countries. After this stratification, the associations between personal characteristics and diarrhea during the first two weeks of their stay were evaluated using logistic regression models. Among participants in intermediate-risk countries, teenagers, males and those with overseas travel experience were associated with an elevated risk of diarrhea; the odds ratios (95% confidence intervals) were 2.42 (1.08-5.43) for teenagers (vs. twenties), 1.93 (1.08-3.45) for males (vs. females) and 2.37 (1.29-4.33) for those with overseas experience (vs. none). Even restricting an outcome to diarrhea during the first week did not change the results substantially. The same tendency was not observed for those in the low-risk countries. Teenage students, males and those with overseas travel experience should be cautious about diarrhea while studying abroad, specifically in intermediate-risk countries